The invention relates generally to a process for making a catalyst and particularly to a process for preparing a catalyst powder and using the catalyst powder in a catalytic convertor.
In selective catalytic reduction (SCR), nitrogen oxide (NOx) reduction can be accomplished with either ammonia or urea, co-fed into the exhaust as these gases pass over a solid catalyst. High NOx reduction conversion has been reported for both ammonia and urea-SCR. However, both the ammonia and urea reduction approaches require infrastructure to supply reductants, and where ammonia is used it may slip past the catalyst, resulting in unacceptable ammonia emissions. Another technology is hydrocarbon (HC) SCR wherein hydrocarbon serves as the reductant for NOx conversion. Hydrocarbons employed for HC-SCR include relatively small molecules like methane, ethane, ethylene, propane and propylene as well as linear hydrocarbons like hexane, octane, etc.
The injection of diesel or methanol has been explored in some of the heavy-duty diesel engines to supplement the HC in the exhaust stream. From an infrastructure point of view, it would be advantageous to employ an on-board diesel fuel as the hydrocarbon source for HC-SCR. SCR using diesel injection may include catalytic metals disposed upon a porous substrate. The preparation and deposition of the catalytic metals on such substrates are typically involved and complex. The structure and/or efficacy of the catalyst substrate is at times compromised during this process, resulting in the catalyst not functioning properly and leading to a reduction in the conversion efficiency of the catalyst.
Therefore, it is desirable to have a method of preparing and processing catalysts that do not compromise the catalyst activity during NOx reduction. It is further desirable to have a process that is amenable for a large-scale production of the catalysts and employing them in the catalytic converters.